Document WO 2012/025874 A1, the entire disclosure of which is hereby incorporated by reference, discloses an audio system that comprises an electro-acoustic transducer or speaker with a housing that forms a resonance volume to improve the quality of the emitted sound. Such speakers are used in mobile devices and there is a continuous need to reduce the size of the housing of the audio system as much as possible while keeping the quality of the audio parameters of the speaker and of the sound emitted. Mobile phone manufacturer define the volume and size of the recess for the audio system in the mobile phone where the speaker with its housing has to fit in. The audio system disclosed in WO 2012/025874 A1 comprises a granulate of ball shaped zeolite material that fills part of the resonance volume. Zeolite material is a sound absorbing material which results in a virtual acoustic enlargement of the volume of the resonance space by at least a factor 2. As a result, the volume of the housing of the speaker that comprises the block of zeolite material can be made smaller compared to a housing of a speaker filled with air.
The housing of a speaker like the housing of a mobile phone nowadays is realized by injection molding of plastic material pressed into an injection mold while the plastic is heated up and moldable. For every change of the form of the housing a new injection mold has to be manufactured what takes some weeks of work with high cost involved.